.github/compose/ci.docker-compose.yml: Reinstate format checking with black
diff --git a/.github/compose/ci.docker-compose.yml b/.github/compose/ci.docker-compose.yml
index cb85f3d..64247c9 100644
--- a/.github/compose/ci.docker-compose.yml
+++ b/.github/compose/ci.docker-compose.yml
@@ -99,7 +99,7 @@
 
   lint:
     <<: *tests-template
-    command: tox -e lint
+    command: tox -e lint,format-check
 
   mypy:
     <<: *tests-template